Method of and apparatus for testing visual acuity.



M. B. CLASON.

METHOD OF AND APPARATUS FOR TESTING VISUAL ACUITY.

APPLICATION FILER OCT. l8, I915.

Patented Mar. 7, 1916.

2 SHEETS-SHEET] QbH'n-eomzo \M w MN M. B. CLASON.

METHOD QF AND APPARATUS FOR TESTING VISUAL ACUITY. APPLICATION FILED OCT. 18.1915.

1,174,547., Patented Mar. 7, 1916.

2 SHEETS-SHEET 2- placed if'using an iinrrnn STATES PATEnT FF C MILO dnAso-mor COLUMBUS, GEO-Rem.

METHOD OF AND APPARATUS FOR TESTING- VISUAL ACUITY.

To all whom it may concern:

Be it known that I, MILO B. CLAs'oN, a citizen of the United States, residing at Columbus, in the county'of Muscogee and State of Georgia, have invented certain new and useful Improvements in Methods of and his vision according to.the siz'eof the procharacter and the distance of the pa-" jected tient from the background at the time of the examination. I The apparatus in brief comprises novel means whereby the test characters'may be projected individually, or in related groups, upon a suitable background, and such characters can be gradually enlarged or diminished in size while remaining in focus;'indica-ting means, controlled or'varied by the adjustment of the lenses. I This novel appa ratus should be'located in a position convenient for the operator and at a predeter mined distance from the background and the patient seated about the usual-distance from the background, that he wouldf be ordinary visual chart;

. then when the patlent can-easily and clearly read the character projected on the'screen,

the operator can deter 'ne bythe indicating means-athe acuity of vision'of-the'pa-z 'tient.-,

' The projected characters are used in place of the ordinary printed or painted charts and in such manner that insteadof the patient havin to-select from a massof characters of different size and kind, simultaneously' exposed to his vision, that one which he thinks he can best distinguish among the lot, his attention 1s.d1rected=to-- ward, and he can only see, one character, or

Specification of Letters Patent.

declare that the following 1s a. full,

' in brief consists in locating a erson at apredetermmed distance from a.

or related'group of while retaining frontpf the slide and shutters,

'mentary and projecting lenses.

related set of characters, (at the will of the v operator) at a time, as the same are projected upon the'screen during the examination, no other unrelated characters being visible to him at the time.- 1

, At'the outset of the examination the operator can readily manipulate the parts quickly until-he projects a character approximately the range of the patients capability of vision; then by novel means "such characterv may be variedin size, while kept in focus; and when the apparatus is adjusted so .acter dlstinguished'by him, the operator by" that the patient declares such charlooking at the indicator (which is autoinatically operated or varied by the adjustment".

Patented Mar. 7,1916. Application filed October 18, 1915. Serial No. 56,442. i

of the lenses) can tell the exact acuity of vision of the patient.

' The method and apparatus-are employed simply to determinethe acuity of vision of.

sensitive and can easilydetect and measure f a with mathematical exactness most minut evariations inacuity of vision. Y Slidesfcon- 'taining variouscharacters suitable forthe testing of eyes of children and illiterates may be provided; also tecting astigmatism.

' The accompanying slides suitable for dedrawings illustrate one practical embodiment of the invention, it

being understood that the invention not limited to the specific forms,dimensifdns or Y constructions of parts shown in. the-drawings, as these are susceptible of variation the essentially novel characteristics and benefits of the'inventio'n.

n The'complete apparatus shown comprises a lamp box, condensing lenses, a slide holder in front of the condensing lenses, adjustable shutters preferably arranged in rear of the slide, a supplementary adjustable lensin and an ad-. justable projecting system of lenses in front of the supplementary lens; the parts being.

so arranged that the light will'be projected in 'the shutters, the sllde-and the supple- Alsonovel means for adjusting the supplementary lens and projecting system together and relatively to each other; and 'a'eprovided whereby the acuity of vision, a fter it has been ascertained by usmg the ap aratus, can be noted by the operator.

n said drawings: Figure 1 is a side eleva- 4 through the condensing lenses, the opening suitableindicating means 7 75 the patient andthe apparatus is extremely as the opening 4;

tion of the complete apparatus. Fig. 2 is an enlarged vertical transverse section on line 2-2 Fig. 1. Fig. 3 is a similar section on line 33, Fig. 1. Fig. 4 is an enlarged longitudinal central section through the adjustable lens portion of the apparatus. vFigs.

5 and 6 are detail views of the adjustable connected in the usual manner with an electric lighting system.

In front of the lamp house is a condensing lens 1, of any suitable. kind, through which the light is'transmitted. The lamp house and condensing lens are preferably mounted upon a frame 2 upon which the other operative parts of the apparatus are also mounted; and said frame may be of any suitable construction adapted to. support the parts and enable the entire apparatus to be conveniently handled as a unit.

Mounted upon the frame 2, in front of the condensing lens 1, is abox 3 in which the shutters and slides are adjustablyf mounted. The box is provided with preferably vertically disposed flanges 3 adapted to guidethe slide S, hereinafter explained: and bow springs 3 may be provided to hold the slide in any adjusted position by friction.

A pair of adjustable shutters 4 and 5 are preferably arranged to slide laterally through suitable openings 3 in the sides of the box 3. Shutter 4 may be provided-with flanges 4* on its top and bottom edges forming guides for the shutter 5, so that the latter is practically adjustable with and also adjustable upon the shutter 4. The shutter 4 may be provided with a projecting handle 4* and the shutter with a handle 5 by which they can be conveniently manipulated. The shutterfl is also provided with an opening 4; and the shutter 5 is provided with a narrow slot 5, and with adjacent wider slot 5 which slots are in the same horizontal plane and when the shutters are in place by properly shifting shutter 5 either of the slots 5 or 5 can be brought into register with the opening 4- in shutter 4, and thus an opening-of greater or less extent or size can be formed throughv the shutters through which openingthe light passes from the condensing lens through the slide. The shutter 4may also be provided with auxiliary muscle test: apertures indicated at 4, through which the transmitted if desired.

Mounted in front of the shutters and slide member 8 light can be are preferably two supplementary lenses 7 and 7 the lens 7 being convex, and the lens 7 concave. These lenses are adjustable so that either can be moved into operative position. These lenses may be mounted on swingable arms 7 and 7 respectively, which arms are pivotally attached to an adjustable member 7 which may be slidably supported on guides 2 on the frame 2; and this member 7 can be adjusted toward or from the condensing lens for the purpose herein after explained.

Mounted upon the frame 2 in front of the said supplementary lenses 7, 7 is a projecting lens or lens system 8, of any suitable kind; and this projecting lens is preferably mounted on a movable member 8, which may also be slidably mounted upon the guide 2. The projecting lens 8 is adjustable toward or from the supplementary lens 7, 7*, as and for the purpose hereinafter explainedl Any suitable means for adjusting the supplementary lens and the projecting lens may be employed; by which the'supplementary lens and the projecting lens can be independently and simultaneously adjusted; it being essential that the projecting lens be adjustable longitudinally of the frame and relatively to the supplementary lenses with 5 variable speed in order toimaintain an exact focus of the character projected in all positions. V

In the drawings a rotatable threaded shaft 9 is shown extending longitudinally of the frame and supported at its ends in bear ings9 9 of any suitable kind on the frame. The portion of shaft 9 adjacent the member 7 is provided'with a spiral channel 9* .ofregular pitch, which channel may be engaged withmember 7 as by a pin 7 attached to member 7 so that by turning shaft 9 the member 7 d and lenses thereon can be moved on the frame toward or from the condensing lens or toward and from the projecting lens. The shaft 9 is also provided with an irregular spiral channel 9 which is reverse to channel 9 and isof greatest pitch at its end adjacent channel 9 and decreases in pitch as it recedes. toward the outer end of the shaft. This channel 9 is adapted to be operatively engaged with as by pin 8 on member 8 and when so engaged by rotating shaft 9,1ens 8 will be moved lineally toward or from the lenses 7, 7 but at a different rate of speed. The shaft 9 is also provided with a spiral channel 9 adjacent the outer end of channel 9 ,and ofirregular pitch but ofless irregularity than the channel 9 and re-'125 verse thereto. The adjacent ends of channel 92, 9 may be connected by a groove 9 so that pin 8 may traverse through groove 9 from channel 9 to channel'9 'or vice versa. The object and use of these various spiral channels will be hereinafter explained. The shaft 9 is also provided with a Worm thread 9 which engages a worm wheel 10 on a transverse shaft 10 journaled in the frame so that this shaft 10 will be rotated when the shaft 9 is operated. The shaft 9 may be operated by any suitable means, as shown a milled disk 9 is pinned to'its outer end by which it can be readily operatedby hand. If desired member 7 may have its under side provided with a depending U-shaped bracket portion 7 adapted to loosely embrace the shaft 9 and insure longitudinal movement of the member 7 when the shaft is rotated. Similarly member 8 may be provided with a depending U-shaped portion 8 adapted to partially embrace shaft 9 and insure longitudinal movement of the member 8 when the shaft 9 is rotated.

In the construction shown in Fig. 4 either the member 7 carrying the supplemental lens 7 or 7*; or member 8 carrying the proj ecting lens 8, can be quickly adjusted longitudinally of the shaft 9, so as to avoid the necessity of rotating said shaft a number of times if it is desired to adjust either or both said members a considerable distance lengthwise of the shaft: or if it is desired to adjust the member 8 carrying the projecting lens from engagement with the channel 9 into engagement with the channel 9 Suitable indicating mechanism is provided, andoperated by or upon the adjustment of the parts, whereby after the parts are finally ad usted to dis lay a character best suited .to the patients vision, the operator can d so readily determine his acuity of vision and record. such position of the parts. Such an indicating mechanism is conventionally illustrated in the drawings and comprises a scale 8 on the frame 2 adapted to be traversed by a pointer 8 on' member 8*" when said member is engaged with the channel 9 of the shaft 9; and the divisions of scale 8" are spaced in proportion to the pitch of the channel 9"; so that when the pin 8 is in engagement with the channel 9 the meme ber 8 would be moved one division of said scale for each rotation of shaft 9 and in accordance. with the pitch of said channel.

A second scale 8 on the frame is adapted to be traversed by the pointer 8 on the memher 8, when said member is engaged with the channel 9 on the shaft 9; said scale 8 being divided according to the pitch of the channel 9, so that: when the pin 8 is in engagement with the channel 9 the member 8 of the shaft 9. In order to obtain a still finer reading of the adjustment of member 8*, I preferably employ a metric indicator of any suitable kind. This I indicator is shown conventionally in Figs. 1 and 3 and will be shifted the length of a related division of said scale 8 for each rotation has a shaft driven from the shaft 10 by shaft llfwill indicate on the dial l1 the fractional part of the movement of member 8 with regard to each division of the scales 8" or 8. The scales and indicating devices should be accurately constructed and calculated so that the scales 8 and 8 will show the length of travel of the projecting lensfor each rotation of shaft 9, and the indicator llindicate the fractional part of any division of scale 8' or scale 8 traversed by the member 8. After the parts have been once adjusted to any particular position, and the indicated position of such partsnoted, such parts can be readily replaced in the same positions if it should be desired to subsequently repeat the test. I

The slide S is preferably composed of a frame 12 (Figs. 7 and 8) adapted to contain a transparent plate 12 upon which the characters are negatively or positively printed in any suitable manner. A set of such transparent plates removably and interchangeably fitting in the frame 12, may be provided. Each of these plates 12 bears a character or series of characters in the desired sequence or arrangement;. so that any desired character may be readily displayed. I have simply indicated in Fig. 7 a plate 12? provided with series of test characters like those used on ordinary visual test charts. Any one or more of the characters on a plate can be displayed at will by the operator by adjusting the slide and the shutters 4 and 5. Obviously a film bearing the desired characters could be used as and in place of the slide, and I consider such a film the "name it correctly, from memory or its association with other known characters rather thanby true or distinct vision. In

my invention however only. suchv a letter or character or related group of characters is displayed to the view of the-patient at one time as the examiner desires to have him see, and the examiner is able to magnify or diminish such characters imperceptibly as much as'needed, and this greatly facilitates obtaining quick and accurate knowledge of the limits of the patients vision; and the patient is not confused by being showna number of unrelated characters simultaneously, and is therefore able to speak with certainty as to whether or not he can clearly see the character displayed.

Persons affected with astigmatism more readily recognize certain letters or characters than others, according to the degree and kind of the astigmatism present, and for' such patients a slide depicting selected letters or characters suitable for astigmatic tests should be used, and the ability of the tween the instrument and the background;

the patient may be seated, and the operator seated beside the instrument where he can conveniently manipulatethe parts so as to project upon the background any desired character which he may wish to use in test- .ing the patients eyes.

It is important vfor the success of my method and apparatus, and the standardizing of such method and apparatus, that the distance between the projecting apparatus and the background be predetermined and fixed so that different operators can use a similar apparatus with similar accurate results. The spiral channels 9 and 9 are mathematically calculated so that while they effect the shifting of the supplementary lens and the projecting lens as described, the focus will bemaintained and the projected character will not be blurred or distorted, although it will change in size; but such change will be gradual and uniform and the character will 'grow or contract uniformly,

and more or less slowly, according to the speed of rotation of the shaft 9. The scales and indicating devices should be mathematically calculated and accurately constructed so that the scales 8 and 8 will show the length of travel of the projecting .lens for each rotation of shaft 9; and indi cator 11 indicates the fractional part of any division of scale 8 or scale 8 traversed by the member 8 The principal object of these scales and indicators being to register the exact amount of magnification or diminishing of the character displayed upon the screen; and by consulting the scales and indicators after any exposure the operator is able to tell the exact size or dimension of the character then exposed and record same. And at any time thereafter by consulting such record can readjust the parts in exactly the same position. With such an apparatus having a set of properly selected and character slides or films a great number of characters may be successively quickly displayed to a patient; and any of such characters can be magnified or diminished at will.

Operation: Preparatory to making a visual test the apparatus'should be fixed at the predetermined distance from the background or screen, and the projecting lens adjusted to about the position shown in full lines in Fig; 4:, intermediate the channels 9 and 9 so it can be readily engaged with either, and the supplementary lenses 7, 7

turned out of the way. The patient being seated in required position, the operatorsuccessively projects upon the screen different characters from a selected slide S until a character becomes distinguishable to the patient. Then the shutters are adjusted so that only a single character, or relative group of characters is displayed to the view of the patient excluding all unnecessary characters confusing to the patient. The shutters can be readily shifted so that the examiner can rapidly determine the characters that are easily distinguished by the patient from those that are distinguished with diificulty. The procedure is adopted under ordinary refractive cases. The proper supplementary lens is then adjusted in place and a character of the size indicated by the preliminary test is displayed; then by adjusting the lenses the size of such character is increased or diminished gradually and minutely until the operator correctly determines what is the smallest possible character the patient can see; and when the parts.

are so adjusted the operator by consulting.

the scales can mathematically determine the acuity of vision of the patient being tested. If for example the patient can readily distinguish characters of a standard size, it is necessary in order to test his acuity of vision to employ character's smaller in size than standard, andtherefore the, diminish ing or concave supplementary lens 7 would be shifted into position to focus with the projecting lens, and the member 8 the latter would be shifted into engagement with the inner end of'the spiral channel 9 Then by rotating shaft 9 both lenses '2' and 8 may be simultaneously shifted away from the condensing lens, but owing ferent pitches of the spiral channels 9 and 9 the projecting lens will move more slowly than the supplementary lens so that the focus will be maintained. By turning shaft 9 backward or forward the projected character can be diminished or increaseduntil the operator satisfies himself that the patient properly sees the character displayed; and the operator can then tell'by observing the position of the pointer 8 scale 8 and the pointer of the hand 11 the smallestf'character which would be visible to the patient at a certain distance, and from the scale and indicator readings the operator can determine the subacuity' of vision of carrying to the difrelative to the the'patient. And by recording such readings in maklng a subsequent test of the same patient he can adjust the lenses in accordance with such, record in the same position they occupied at the time of such record and thus be able to make reliable comparative tests. 1 If thepatlents approximate range of vision should be below the standard; the enlarging or convexsupplementary lens 7 should be positioned in focus with projecting lens 8, and the latter shifted so,'that the'pin 8 enters the outer end of the spiral channel 9.

Then by turning the shaft 9 the'lenses 7 and 8 will be moved toward each other; the lens 8 however traveling toward the lens 7 with gradually increasing speed so that the lenses will be maintained in true focus in all positions. Such shifting of the lenses toward each other results in a gradual enlargement of the character projected on'the screen or background; and without requiring the patient to move to or from the screen the same result is obtained as if he was to-movecloser to or farther away from the screen. The operator adjusts the apparatus until he is satisfied thatthe patient can properly see the character displayed, and when such adjustments have .been made he can byobserving the scale 8 and indicator determine What is the exactacuity of vision of the patient and make suitable records for future comparison.

This method and apparatus is especially useful in measuring the acuity of vision of illiterates and children who have not been taught to' read, as special can be .used and such objects projected on ually grows larger and more clear,

ground and enlarging or diminishing such the person,

1. The herein describedmethod of-testing. human eye-sight consisting in projectinga selected character upon a suitable back character while maintaining it in'focus until it is clearly visible to the'person being tested,.thereby determining the visual acuity of substantially as described.

2. The herein described process of testing human eye-sight consisting in locating a person at a back-ground a character, and enlarging'or diminishing such character untilit is clearly seen by the person, and mathematically determining the acuity to the size of the projected character and the slides depicting. objects familiar to illiterates or children suitable distance from a suitableback ground, and projecting upon such ofhis vision according &

ground.

3. The-herein described process of test-- ing human eye-sight consisting in locating a person at a predetermined distance from a suitable back-ground; projecting upon such back-ground a character, or related group of characters, and enlarging or diminishing such character while maintaining it focus until it is clearly seen by the patient, and mathematically determining the acuity of his vision of the projectedcharacter and the distance of the patient from the back-ground.

:4. Apparatus for testing human eye-sight comprising means for projecting a selected character upon a suitable back-ground, and means for varying the size 6f the projected character while maintaining the focus. i 5. Apparatus for testing human eye-sight, comprising selected test characters, or related groups of test. characters, and means according to the size for successively projecting same upon a ground, with means for varying the size of the projected character while maintaining such character in focus. v 7. Apparatus for testing human eye-sight lated groups of test characters, and means for successively projecting upon a suitable back-ground a single selected test character, or related groups oftest characters, until a character or group clearly visible to the person being tested is varying the size of; while maintaining the acuity. of vision being determined ac? cording to the size of the projected character and the distance ofthe patient from the screen.

8. Apparatus for comprising means character upon a suitable back-ground, including a projecting lens, a supplementary lens, and means for relatively adj usting'said lens to vary ter while maintaining the focus.

9. Apparatus for testing comprising means for projecting a selected the projected character character upon a suitable back-ground -including a projectmg' lens, a supplementary lens, and. means .for ad usting said lens simultaneously at different relative speeds to vary the size of the projected character while maintainingthe focus.

.10. Apparatus for determining visual acuity of the human eye, comprising a procomprisingselected test characters, or refound; with means forv for projecting a selected human eye-sightsuch character in focus;

testing human eye-sight the size of the projected charac- Hjecting apparatus including a jecting apparatus including a projecting lens and a supplementary lens interposed between the illuminating means and the projecting lens, and means for relatively ad 'usting said projecting and supplementary lens to vary the size of the character projected on the screen while maintaining the focus.

11. Apparatus for determinlng visual acuity of the human eye comprising a p rorojectlng lens, a condensing lens and a supp ementary lens interposed between the condensing lens and the projecting lens, said projecting and supplementary lens being both dependently and simultaneously adjustable to vary the size of. the character projected on the screen while maintaining the focus.

12. In apparatus for determining the visual acuity of the human eye; the combination of a light box, a condensing lens, a slide bearing test characters, and means for varying the passage of light through said slide; with a projecting lens, a supplement'ary lens interposed between the condensing lens and the projecting lens, and

' between the slide and the means for adjusting said projecting and supplementary lens to vary the size of the character projected on the screen while maintaining the focus.

13. In apparatus for determining the visual acuity of the human eye; the combination of a light box, a condensing lens, a slide bearing test characters, andshutters for varying the passage of light through said slide; with a projecting lens, a-supplementary lens interposed between the screen and the projecting lens, and means for simultaneously but unequally adjusting said p'rojecting and supplementary lens to vary the size of the character projected on the screen while maintaining the focus.

14. Apparatus for determining the visual acuity of the human eye, comprising a projecting apparatus including a projecting lens and a supplementary lens interposed projecting lens,

said projecting and su plementary lens be-.

ing simultaneously ad ustable to vary the' size of the characterprojected on the screen while mamtaining the focus; and means operated by the adjustment of said lens whereby the acuity of vision is indicated.

15. Apparatus for testing human eye sight, comprising selectedtest characters, or related groups of test characters, and

' means for successively projecting same upon a suitable background until a character or group is found which determines the acuity of vision of the patient whose sight is being tested; and means whereby the acuity .of

. vision is indicated.

16. Apparatus for testing human eyesi' ht comprising selected test characters, or re ated groups of test characters, and means bearing test characters,

'means operated by the .or related groupof test characters, until a character or group clearly visible to the person being tested is found; with means for varying the size of the projected character while maintaining such character in focus, the acuity of vision being determined according to the size of the projected character and the distance of the patient from the screen; and means operated by the adjustment of said lens whereby the acuity of vision is indicated.

18. In apparatus for determining the visual acuity of the human eye the combination of a light box, a condensing lens, a slide and means for varythrough said screen; a supplementary lens ing the passage of light with a projecting lens, interposed between the condensing lens and the projecting lens, said projecting and supplementary lens being adjustable to vary the size of the character projected on the screen while maintaining the focus; and adjustment of said lens whereby the acuity of vision is indicated.

19. In apparatus for determining the visual acuity of the human eye; the combination of a light box, a condensing lens, a slide bearing test characters, and shutters for varylng the passage of light through said slide; with a projecting lens, a supple mentary lens interposed between the -screen and the projecting lens, and means for simultaneously but unequally adjusting said projecting and supplementary lens to vary 1 the size of the character projected on the screen whlle maintaining said lens in focus, andmeans. operated by the adjustment of said lens whereby the acuity of vision is indicated.

20. In an apparatus of the character specified, the combination of a light box, a condensing lens, a slide, and means for controlling'the light through the slide; with a pair of adjustable supports, lenses mounted on said supports, and a rotatable shaft havlng spiral channels operatively engaged with said supports whereby said supports may be simultaneously operated.

In an apparatus of the character specified, thecombination of a light box, a condenslng lens a slide and means for controlling the light through the slide; with a pair of adjustable supports, lenses mounted on said supports, and a rotatable shaft having spiral channels operatively engaged shaftadjacent these supports having spiral channels of different pitch adjacent the respective supports, and means on each support engaging the related channel, whereby when the shaft is rotated said supports are moved oppositely but at different speeds to maintain the focus; and'mechanism whereby the amount of movement of the said holders by the rotation of said shaft is. indicated.

23. In an apparatus ,of the character specified, the combination of a light box, a condensing lens, a slide and means for controlling the light through the slide; with a pair of movable lens supports, a rotatable shaft adjacent these supports having spiral channels of different pitch adjacent the respective supports, and means on the said supports engaged with the related channels, whereby when the shaft is rotated said supports are moved oppositely but at different speeds to maintain the focus.

24. In an apparatus of the character specified, the combination of a projecting lens holder, a shaft adjacent said holder having adjacent oppositely extending spiral channels, means on the said holder whereby it may be engaged witheither channel, and

means for rotating said shaft, each of said channels being of varying pitch.

25. In an apparatus of the character specified, the combination of a light box, a condensing lens, a slide and means for controlling the light through the slide; with a pair of movable lens supports, a rotatable shaft having spiral channels adjacent the respective supports, one of said channels being regular and the other channel of varying pitch, and means on each support engaging the related channel whereby when the shaft is rotated said supports are moved oppositely but at different speeds; with mechanism whereby the amount of movement of the said supports by the rotation of said shaft is indicated.

In testimony that I claim the foregoing as my own, I aflix my signature in presence of two witnesses.

MILO B. CLASON.

Witnesses:

ARTHUR E. DEWELL, W. WALLACE NArRN, Jr. 

